Hi all, We have that feature in our port which we would like to contribute, and I would like to gauge opinions.
First off, I am not sure which list is correct. This is more of a serviceability issue, but implementation wise it fit hs-runtime better. I'll start with serviceability, but feel free crosspost if needed. Second, I am aware that this may require a JEP. If necessary and the feedback is positive, I will draft one. ---- In our port we have something called "Statistics History". Basically this is a rolling history, spanning up to 10 days, of a number of key values. Key values range from JVM specifics like heap size, metaspace size, number of threads etc, to platform specifics like memory footprint, cpu load, io- and swapping activity etc. A periodic tasks collects those values, in - by default - 15 second intervals. They are then fed into a FIFO. FIFO spans 10 days. To save memory that FIFO is downsampled in two steps, so we have the last n hours in high resolution and the last n days in low resolution (of course all these parameters are configurable). The history report can be triggered via jcmd, and also could get printed in the hs.err file (open for debate). --- Here some examples of how the whole thing looks like: http://cr.openjdk.java.net/~stuefe/webrevs/stathist/examples/stathist-volker.txt http://cr.openjdk.java.net/~stuefe/webrevs/stathist/examples/stathist-s390x.txt --- This feature has been really popular with our support folk over the years. Be it that the VM is starved for resources by the OS, that we have some slow- or fast developing leak situation etc: these values are a first and easy way to get a first stab at a situation, before we start more expensive analysis. The explicit design goal of this history was to be very cheap - cheap enough to be *always on* and getting forgotten. It is, in our port, enabled by default. That way, if a problem occurs at a customer site, we immediately see developments spanning the last 10 days, without having to reproduce the issue. It is also robust enough to be usable during error reporting without endangering the error reporting process or falsifying the picture. I am aware that this crosses over into JFR territory. But this feature does not attempt to replace JFR, it is intended instead a cheap always on first stop historical overview. -- I have a patch which can be applied atop of jdk12: http://cr.openjdk.java.net/~stuefe/webrevs/stathist/stathist.patch It works, passes our nightlies and no regressions are shown in dapapo benchmarks. Please tell me what you think. Given enough interest, I will attempt to contribute (drafting a JEP if necessary.) Thanks and Kind Regards, Thomas
